This invention relates generally to the production of filamentary material and more particularly to a novel spray spinning nozzle for spinning molten synthetic resinous material to form a nonwoven structure.
Various apparatus has been developed in the past to create an integrated system for forming a fibrous assembly, such as a nonwoven fabric or the like, directly from a molten synthetic resinous material. Typically, such an apparatus may use an extruder in which a synthetic resinous polymeric material is plasticated under the influence of heat and pressure to form a quantity of molten material which can then be forced through a nozzle orifice as a continuous liquid filament. Each of a plurality of high velocity gaseous jets is directed along the freshly extruded filament at a shallow angle to create a drag force for attenuating the filament which is then carried along by the attenuating gaseous jets and deposited on a collection surface to form a nonwoven structure. Such a device in the past has been known as spray spinning apparatus because the filamentary material appears to be sprayed against the collection surface.
The attenuating gaseous jets contribute to filament cooling in addition to both attenuating and conveying the filament to the collection surface. Since the filament of polymeric material is still in a somewhat molten or tacky stage as it strikes the collection surface, some sticking together occurs at each point where filament contacts itself. Also, the filament may loop about and stick to itself.
One such spray spinning apparatus is shown in U.S. Pat. No. 3,849,040 which is assigned to the assignee of the present patent application. This patent shows a stream of filamentary material emanating from a nozzle. A pair of elongated attenuating gas jets, each with a rectangular cross section, are placed on either side of the nozzle. The gas jet outlets are both in the same plane perpendicular to the nozzle axis, are positioned forwardly of the nozzle orifice and the gas jets therefrom intersect at a point offset from the nozzle axis in the plane of the nozzle axis. The axial component of the drag forces produced on the filament by the gas jets attenuate the filament. Great care must be taken to control the geometry of the gas jets to provide a proper distribution in the collected filament.
One disadvantage of this system is that the angles of the gas jets require adjustment when the gas pressure or polymer flow rate is changed. Thus, careful and time-consuming control of the gas pressure and gas jet angles is required.
The molten polymer and the attenuating gas do not flow through the same nozzle. The gas jets are separated from the nozzle orifice by an insulating means such as an air space. As a result, the gas jets produce a low pressure area near the nozzle orifice which induces a flow of ambient air past the nozzle. This induced flow tends to convectively cool the nozzle and to cause the molten material to harden and obstruct the orifice: known as nozzle freeze-up.
Another disadvantage of such apparatus relates to the difficulty in controlling the spray pattern. The filament seems to wander causing an unduly broad and unfocused spray pattern. Accordingly, positioning of spray spinning nozzle for product uniformity is difficult.
In the past it has been necessary to use high throughput rates of polymeric material through the nozzle to reduce nozzle freeze-up. This produces a thicker filament, requires higher gas supply pressure to obtain higher momentum in the attenuating gas jets, and requires the distance between the nozzle orifice and the collection surface to be greater than desired. As a result of these higher operating parameters, the nonwoven structures produced by present spray spinning apparatus have not been entirely satisfactory. The filament is relatively thick and also includes quantities of "shot" which is solid debris or beads of non-attenuated material which increase cost and weight of a product and undesirably affect the feel of the nonwoven product. Unformity of filament thickness and spray pattern has been difficult to attain and maintain. Collection can be difficult and attenuation efficiency has been low. Under these conditions overall operation can be difficult.
During start-up of a horizontal spray spinning system, the plasticated synthetic resinous material passes through the nozzle orifice and is allowed to drop without attenuation. When time-wise steady temperature and flow conditions are obtained, the gas jets are brought into operation to attenuate and convey the filament to the collection surface.
Also, during operation of the spray spinning apparatus, aberrant performance of a spray spinning nozzle may necessitate abrupt interruption of the action of the gas jets to avoid ruining a product being manufactured.
When the air manifold can only be removed axially from the nozzle through which the synthetic resinous material is extruded, removal of the manifold is accompanied by depositing material thereon. The deposited material may interfere with actual assembly of the manifold on the nozzle and may accumulate in a sufficient quantity to interfere with actual operation of the nozzle.
Should the nozzle discharge polymeric material upstream of the gaseous jet exhaust, then the starting problem is further exacerbated. In addition, the potential for polymer accumulation in the event of malfunction during operation is substantially heightened. Where the gas manifold is annular, the material accumulation is generally a problem.
Another significant problem with spray spinning nozzles relates to the manner in which orifice blockage can be removed. Generally, substantial disassembly of the nozzle is required. In fact, in many instances, the entire spray spinning nozzle must be removed from the source of polymeric material and disassembled. With a small diameter extrusion orifice, the likelihood of blockage and freeze-up is materially increased.
Accordingly, it will be apparent to those skilled in the art that there continues to exist a need for a spray spinning nozzle assembly which overcomes problems of the type discussed above.